$5© On fhe iforthern Magnetic Pok of th'e EartS. 



turn there was 19" 44' weft. In the fuppofition that the lines 

 of dire<?tion lie in the planes of great circles, and meet ia 

 one point, J found it to be in 77° 4' north lat. Euler in the 

 ]\Iemolrs of the Academy of Berlin places it in 75*^ ; Le- 

 monnier, in iht Lois tlu Mag7ietifmc, in 73^; and Euft'on, 

 in 71"; which makes the differences to be very fniall. Eu- 

 ler conceived two magnetic pole*, which are not diametri- 

 cally ojjpofite to each other. The two obfervations which 

 form the ground of my calculation were made, however, 

 near enough to the north pole to enable us to determine it 

 independently of the fonth pole. Churchman places the 

 north pole in the lat. of 60"^; a difference which would be 

 too great. 



The two obfervations here alluded to would give tlie longi- 

 tude of the magnetic pole in too doubtful a manner, as the 

 angle at the pole is too obtufe. I endeavoin-ed, therefore, to 

 obtain an intermediate obfervalion, and found that, in the 

 year 1770, at Norreton, in lat. 40" 10' north, and long. 77" 

 36' weft from Paris, the declination was 3° 8' *. From this 

 it would follow, that the longitude of the magnetic pole is 

 lie" ^^' weft from Paris. The year, however, of the laft 

 obfervation does not eorrefpond with that of the two former 

 ones : but the difference on this account cannot be of much 

 importance. 



At the time of the tranfit of Venus over the fun's di(k in 

 1779, obfervcd at ITudfon's Jjay, in lat. ^(3° 48' north, and 

 long. 96^ 30' weft from Paris, the declination of the magne- 

 tic needle was found to be, in that place, 9° 41' weft f. 

 This gave me for the longitude of the magnetic pole only 

 86° weft from Paris. The mean of the tuo obfervations, 

 therefore, would be 98°. Euler makes the longitude 115°, 

 and Biift'on 100° well from Paris: Lemonnicr makes it only 

 50**. But, as the parallel at fo high a northern latitude is 

 only of fmall extent, a more confiderable difference in lon- 

 gitude would have no great influence on the previous deter- 

 mination of the true pofition of the magnetic pole. 



We can therefore admit the given data till a fcries of 

 more accurate obfervations of the declination of the mag- 

 netic needle, and its variations, collcftcd for different deter- 

 minate places, f.iall enable us to deduce from them the va- 

 riations of the magnetic pole. The variations of the mag- 

 netic declination have been obfervcd at Paris for 140 years; 

 hut as this has not been the cafe in x*iinerica, ue (till want 

 the proper data for calculating the motion of the niagnctio 



* American Tranfaftions, p. 117. 

 t Phil. Trunfattions 1769, p. 4S3. 



pole 



